Processing of solid micron sized particles for rapid deposition on substrate surfaces with uniform particle distribution

ABSTRACT

This application relates generally to a method and apparatus to deposit particles onto one or more coupons, and harvest particles from one or more coupons, which may beneficially provide a more uniform or localized distribution of particles over a specified area on each coupon. The application relates to a method and apparatus for depositing particles onto one or more coupons using a sieve. The application also relates to a method and apparatus for depositing particles onto one or more coupons using a dust storm. The particle loadings achieved on each coupon or across an individual coupon may be substantially uniform. The application further relates to a laser-based method and apparatus for transferring particles deposited at localized points on a source coupon to a different substrate for further use.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 15/479,461, filed on Apr. 5, 2017, which claimed the benefit ofpriority under 35 U.S.C. § 119(e) from U.S. Provisional Application No.62/318,651, filed on Apr. 5, 2016, the contents of both are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

This application relates generally to a method and apparatus to depositparticles onto one or more coupons, and harvest particles from one ormore coupons, which may beneficially provide a more uniform or localizeddistribution of particles over a specified area on each coupon. Theapplication relates to a method and apparatus for depositing particlesonto one or more coupons using a sieve. The application also relates toa method and apparatus for depositing particles onto one or more couponsusing a dust storm. The particle loadings achieved on each coupon oracross an individual coupon may be substantially uniform. Theapplication further relates to a laser-based method and apparatus fortransferring particles deposited at localized points on a source couponto a different substrate for further use.

BACKGROUND OF THE INVENTION

Standoff threat detection provides the capability to detect traceamounts of explosive, chemical, biological, or other agents withoutphysical contact, obviating the need to obtain consent or cooperationfrom targets. Operation of detection equipment may be carried out at asignificant distance, or up close to an object of interest, for example,from 0.5 to 100 meters away, reducing the level of risk posed tosecurity personnel.

Such techniques are possible because the process of manufacturingthreats, such as explosives, typically results in trace residuesincluding particles of the threat material being left on persons andobjects associated with manufacturing process. IR-laser spectroscopy andother techniques may be used to detect trace amounts of chemicals, suchas explosives, which typically exhibit strong absorbance patterns in themid-IR region. In order to calibrate the equipment to accurately detecttrace amounts of threat materials and establish limits of detection forvarious threats, reference materials and standards are needed. Thereference materials and standards may also be used to develop newtechniques and new equipment to more accurately detect threats.Standards having known areal density are also desired, and control overvariables including particle size, shape, and areal distribution wouldbe beneficial. Given the very small amounts and volatility of thematerials involved, production of consistent standard materials isdifficult.

Techniques that may be used to deposit particles for detection,calibration, or further testing include inkjetting, aerosol spraying,pipetting, and spin coating onto a substrate.

Inkjetting has been popularized because of its use in printing, and hasbeen adapted to print other chemicals of interest as a solution whichdries on contact with an intended surface. Inkjetting is largely limitedin its control of particle deposition by the solvent selected and itsinteraction or wetting with a surface. As the solution dries, complexprocesses can occur which may result in a wide variety of results,including coffee ring features, dome structures, isolated arrays ofsub-micron sized particles, polycrystalline structures, and more. Noneof these represent typical particles found in fingerprints because theirsizes and groupings do not match what is produced in an actualfingerprint. In addition, because drops deposited by inkjetting aretypically very small, they evaporate very quickly and may trapsubstantial amounts of solvent in the produced crystal. The shapes,distribution, and content of particles is important in standoffdetection technologies because the optical spectroscopies employed areoften affected by the range of particle sizes involved and theirchemical content. Further, inkjetting is inherently a serial process.

Sieving stacks are routinely used in laboratories to fractionateparticles with one or more sieves. A collection pan is provided at thebase of the stack in order to collect the processed particles. The stackis typically held together using a rigid support structure, and the baseof the stack is positioned on a vibratory plate to couple a vibratoryaction to the sieving stack. The vibration causes the particles to movewithin each sieve and through suitable sieve openings into the receivingcollection pan. An impact hammer action can also be applied to the topof the stack, and is typically operated at 1 Hz to assist the sievingaction and reduce mesh pore blockages. The sieving stacks are typicallyoperated in ambient air, which limits their practical use to particlesof about 20 microns and above.

Using the conventional sieving stacks, the sieving of particles to aloading of between 10-100 micrograms/cm² can take tens of minutes, whichis time consuming if multiple sieving operations are needed. Inaddition, there is no means to compensate for non-uniform sievingthrough a sieve membrane. Non-uniform sieving can result because of poreopening blockages, vibration nodes that form in the sieving membranecausing particle pooling in a sieving pan, and any sieving membrane/panslope that leads to particle pooling towards one side of a sieving orcollection pan. Feedback control to stop particle deposition when adesired amount of particles have been deposited is also lacking. Theselimitations present significant drawbacks when applying sieving or othertechniques to fabricate samples or coupons which require controlledparticle amounts and controlled particle distributions.

U.S. Pat. No. 9,022,220 describes a sieving system that includes afilter, a blade stirring a powder accumulated on the filter, a driverdriving the blade, and a notifier for notifying a user of predeterminedinformation regarding the status of the filter, based on a load on thedriver while driving the blade.

U.S. Pat. No. 8,973,759 describes a sieving device including a hollowcylindrical body, a filter disposed at a bottom portion of the hollowcylindrical body, and a blade configured to rotate in close proximity tothe filter around a rotation axis thereof, crossing the filter tothereby stir powder supplied to the hollow cylindrical body.

Each of these techniques uses a blade to stir and mix a powder presentin sieve, and monitors the sieve for blockages.

However, none of the existing deposition techniques are able toadequately address the problems associated with non-uniform particledeposition, particularly in the context of standoff detectionapplications.

SUMMARY OF THE INVENTION

In contrast to the existing techniques described in the prior art, insome aspects, the present invention beneficially accelerates the sievingprocess while providing greater control over particle deposition. Insome aspects, a blade is provided that is in contact with a sievingmembrane. In other aspects, the invention only loads the sieve with asmall amount of material that barely covers the surface of the sievingmembrane. Accordingly, the products, systems, and methods of theinvention beneficially provide superior sieving performance, includingincreased sieving speed, as well as improved particle distributionacross the surface of a sieve and/or a test coupon. In further aspects,the present invention utilizes a dust storm generating apparatus andmethod to evenly distribute particles. Once an even distribution ofparticles deposited on a substrate has been achieved, additionalapparatus and methods may be used to directly select and depositparticles of interest on substrates in desired patterns.

The invention described herein, including the various aspects and/orembodiments thereof, meets the unmet needs of the art, as well asothers, by providing a method and apparatus to deposit small solidparticles of a known chemical through a sieve, or using a dust stormtechnique, onto one or more coupons in a controlled fashion to produce amore uniform distribution and loading of particles on each coupon. Inthe case of a sieving method and apparatus a more uniform distributionof particles across the sieving membrane may also be achieved.

This invention enables the processing of solid micron-sized particlesfor rapid deposition on substrate surfaces with a substantially uniformparticle distribution. The invention expands the practical range ofsieve mesh openings to below 20 microns, allowing particlefractionations of different size ranges between 0-20 microns, includingbut not limited to 10-20 microns, 5-15 microns, and 0-10 microns. Thisis of particular importance for fabricating test specimens to be used inanalytical applications, such as trace particle detection of explosivesor environmental pollutants.

The sieving apparatus and methods of the invention may be beneficiallyused in conjunction with controlled particle deposition techniques inwhich particles deposited on a test coupon are individually selected forfurther processing.

According to a first aspect of the invention, a sieving apparatus isprovided, including a sieving pan adapted for receiving particles to besieved, which includes a sieve membrane having upper and lower surfacesand a wiper that wipes particles over an upper surface of the sievemembrane. The sieving apparatus further includes a collection pan thatretains particles that pass through the sieve membrane, and a substrateprovided within the collection pan to receive a portion of the particlesthat pass through the sieve membrane. The wiper is moved with respect tothe upper surface of the sieve membrane and applies force to particlesadjacent to the upper surface of the sieve membrane, producing particledistributions on the membrane which for a time averaged basis spend anequal time at their prescribed radius from the center of a circularsieve for the corresponding circular path to produce a substantiallyuniform time averaged distribution of particles across the membrane atthe width of the wiper and accelerating the movement of the particlesthrough openings in the sieve membrane into the collection pan and ontoone or more substrates.

According to another aspect of the invention, a sieving apparatus isprovided, including a sieving pan adapted for receiving particles to besieved, which includes a sieve membrane having upper and lower surfaces.The sieving apparatus further includes a collection pan that retainsparticles that pass through the sieve membrane, a rotating coupon stagehaving a surface adapted to receive one or more coupons, where the oneor more coupons receive a portion of the particles that pass through thesieve membrane, and a vibration generator that generates vibratoryaction to cause particles to pass through the sieve membrane. The couponstage is provided in the collection pan, and is rotated as the particlesare sieved, producing particle distributions that are more uniformacross the one or more coupons when compared to particle distributionsproduced on coupons that are not rotated during sieving.

Another aspect of the invention relates to an apparatus for generating aparticle storm, including a container having an opening to introduce aparticulate substance therein, a fan apparatus provided within thecontainer, one or more coupon substrates positioned within thecontainer, and a cover for sealing the opening of the container. The fanapparatus is actuated to cause particles within the container to form aparticle storm, which deposits particles onto the one or more couponsubstrates.

According to a further aspect of the invention, an apparatus forgenerating a particle storm is provided, including an acoustictransformer configured to generate ultrasonic frequencies, a substrateholder for positioning a substrate having particles deposited thereonadjacent to the acoustic transformer, and a platform for positioning oneor more coupons adjacent to the substrate having particles depositedthereon. The acoustic transformer is actuated to cause particlesdeposited on the substrate to be released from the source substrate andform a particle storm, wherein the particles present in the particlestorm are deposited onto the one or more receiving coupons.

According to a still further aspect of the invention, a particleprinting apparatus is provided, which includes a first movable stageadapted to hold a first source substrate having particles depositedthereon, an imaging system adapted to record a map comprising locationsof particles deposited on the first source substrate, a second movablestage adapted to hold a second substrate designated for receivingparticles deposited on the first substrate, and a laser. A particle ofinterest deposited on the first source substrate is selected using themap recorded by the imaging system, the first movable stage is moved toalign the particle of interest with a beam from the laser, secondmovable stage is moved to align the particle of interest with a locationon said second substrate where the particle of interest is to bedeposited, and the laser is energized, causing the particle of interestto be dislodged from the first substrate and fall onto the location onthe second substrate.

In accordance with another aspect of the invention, a method for sievingparticles is provided, including placing particles into a sieving panincluding a sieve membrane having upper and lower surfaces and a wiperthat wipes particles over an upper surface of the sieve membrane,actuating a vibration generator to generate vibratory action to causeparticles to pass through the sieve membrane, actuating a wiper to moveacross the upper surface of the sieve membrane and apply force toparticles on the upper surface of the sieve membrane, producing particledistributions that are substantially uniform across the width of thewiper and accelerating the movement of the particles through openings inthe sieve membrane, and collecting particles that pass through the sievemembrane in a collection pan having a substrate provided therein,wherein a portion of the particles that pass through the sieve membraneare deposited on the substrate.

According to a further aspect of the invention, a method for sievingparticles is provided, including placing particles into a sieving pancomprising a sieve membrane having upper and lower surfaces and a wiperthat wipes particles over an upper surface of the sieve membrane,actuating a vibration generator to generate vibratory action to causeparticles to pass through the sieve membrane, actuating a rotatingcoupon stage having a surface adapted to receive one or more coupons,where the one or more coupons receive a portion of the particles thatpass through the sieve membrane as the coupon stage rotates producingcoupons having particles deposited therein, wherein the particledistributions on the coupons are substantially uniform, and collectingparticles that pass through the sieve membrane but are not deposited onthe coupons or coupon stage in a collection pan.

According to a still further aspect of the invention, a method fordepositing particles using a particle storm is provided, includingproviding a particulate material in a container through an openingtherein, providing a fan within the container, positioning one or morecoupon substrates within the container, sealing the opening of thecontainer, and actuating the fan to generate a particle storm, causingparticles in the particle storm to be deposited onto the one or morecoupon substrates.

According to yet another aspect of the invention, a method fordepositing particles using a particle storm is provided, includingproviding a particulate substance on a source substrate, placing thesubstrate having the particulate substance thereon adjacent to anacoustic transformer configured to generate ultrasonic frequencies,placing one or more coupons adjacent to the substrate having theparticulate substance thereon, and actuating the acoustic transformer,causing the particulate substance on the substrate to be released fromthe substrate forming a particle storm, wherein the particles present inthe particle storm are deposited onto the one or more coupons.

According to still another aspect of the invention, a method forprinting particles onto a substrate is provided, including providing afirst substrate having particles deposited thereon on a first movablestage, recording an image comprising sizes and locations of particlesdeposited on the first substrate, providing a second substrate forreceiving particles on a second movable stage, selecting a particle onthe first substrate to be deposited on the second substrate using theimage, moving the first stage to align the location of the selectedparticle on the first substrate with the location of a laser beam,moving the second stage to align the location on the second substratewhere the selected particle is to be deposited with the location of theselected particle on the first substrate, and energizing the laser beam,causing the selected particle to be dislodged from the first substrateand fall onto the location on the second substrate where the particle isto be deposited.

Test coupons loaded with particles produced using any of the apparatusor methods of the invention are also provided in accordance with theinvention.

The invention is further directed to the use of any of the apparatus ofthe invention to produce a test coupon loaded with particles.

The invention also relates to the use of a first substrate preparedusing any of the apparatus or methods of the invention in the particleprinting apparatus and method.

Other features and advantages of the present invention will becomeapparent to those skilled in the art upon examination of the followingor upon learning by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the Poisson distribution when the averagenumber of particles in a given area is 1, 4, or 10.

FIG. 2 is a drawing depicting a sieving stack.

FIGS. 3A and 3B are drawings of sieving stacks installed on a shakerplatform, with an impact hammer provided above the sieving stack lid. InFIG. 3A, the coupon platform is contained within the collection pan. InFIG. 3B, a rotating coupon platform and extension sleeve are depicted.

FIG. 4 is an exploded view of a sieving stack and shaker platform withsupport structure.

FIG. 5 is a side perspective view of a collection pan having a rotatingcoupon platform mounted therein, including an extension sieve and mask.

FIG. 6 is a drawing of a collection pan showing recesses to receivedamping feet, and showing a conduit hole, and an opening for an arm.

FIG. 7 is a drawing of a coupon holder in which an electromechanicaldecoupler is provided as a vibration damper.

FIG. 8 is a drawing of a sieving stack provided on a shaker with aseparate vibration isolating arm holding a coupon platform, and aseparate stand for mounting the arm.

FIGS. 9A-9C are drawings of various embodiments of the wiper. FIG. 9A isa wiper having a blade. FIG. 9B is a wiper comprised of multiple bladesegments. FIG. 9C is a wiper having a brush.

FIG. 10 is a drawing of a ball-milling apparatus and controller, with aball-milling container provided thereon.

FIG. 11 is a drawing of ball-milling container provided on the rollersof a ball-milling apparatus, showing the balls contained inside theopening of the container.

FIG. 12 is a drawing of an alternative ball-milling container havingstrips removably mounted to the inner walls of the container.

FIG. 13 is a drawing of an ultrasonic dust storm assembly for creating adust storm using particle-coated strips.

FIGS. 14A-14C are drawings of a dust storm apparatus. FIG. 14A is acontainer housing a fan and a substrate. FIG. 14B is a view of theinside of the container lid showing a substrate platform mountedtherein. FIG. 14C is a view of the substrate platform and substrate.

FIG. 15 is a drawing of an alternative dust storm apparatus in which alid adapted to fit the opening of a ball-milling container includes acoupon mounting portion and a blower attached thereto. The coupon isprovided on the outside of the lid for the container, and is masked byan opening in the lid.

FIG. 16 is a drawing of a laser particle printing apparatus includingmotorized stages for holding a receiving substrate and a particle-coatedsource coupon.

FIGS. 17A-C are photographs of particles deposited using the methods ofthe invention. FIG. 17A shows an inverted image using a 5× objectivelens of a glass coupon coated with DNT particles deposited using thedust storm technique. FIG. 17B shows an inverted image of 20 micron TNTparticles deposited at a density of 6.0 micrograms/cm′ using a sievingtechnique. FIG. 17C shows sieved RDX particles deposited onto asubstrate containing pools of sebum oil.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention described herein, including the various aspects and/orembodiments thereof, meets the unmet needs of the art, as well asothers, by providing a method and apparatus for depositing particlesthrough a sieve, or using a dust storm technique, onto one or morecoupons or substrates. The deposition is controlled in order to producea substantially uniform distribution of number of particles, arealdensity and particle size over the intended area on a coupon substrate.The application further relates to a method and apparatus fortransferring individual or clusters of particles deposited on a couponto a different substrate for further evaluation.

The particles processed in accordance with some embodiments of theinvention may be microspheres or arbitrary-shaped particles of anyorganic or inorganic chemical. Of particular interest are explosives ornarcotics or related materials.

The explosives or explosive-related materials encompass organic andinorganic materials, and may include, but are not limited to,2,4,6-trinitrotoluene (TNT), triacetone-triperoxide (TATP),octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), ammonium nitrate(AN), potassium nitrate (KN), urea nitrate (UN), potassium perchlorate(PP), potassium chlorate (PC),octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX),hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), andpentaerythritol-tetranitrate (PETN).

The narcotics include, but are not limited to heroin, lysergic aciddiethylamide (LSD), marijuana (cannabis),3,4-methylenedioxymethamphetamine (ecstasy), methaqualone, peyote,Vicodin, cocaine, methamphetamine, methadone, hydromorphone, meperidine,oxycodone, fentanyl, Dexedrine, Adderall, and Ritalin. Drug schedulesmaintained and updated by the U.S. Drug Enforcement Administration (DEA)classify drugs as Schedule I, Schedule II, Schedule III, Schedule IV,and Schedule V based on their potential for abuse and dependence.Particles comprising drugs selected from any of these schedules may beused in the apparatus and methods of the invention. In some embodiments,the particles comprise DEA Schedule I or Schedule II substances.

Particles processed in accordance with some embodiments of the inventionmay be taken from visible, UV or infrared dyes, and polymers including,but not limited to polystyrene, polyacrylonitrile, polyethylene,polymethylmethacrylate, polyvinylchloride, nylon, Teflon, polyurethane,polypropylene or silica.

Particles of materials found in chemical and biological weapons may alsobe processed by the apparatus and methods of the present inventionincluding, but not limited to, chemical nerve and blister agentsformulated in porous or adsorbent solid particles or with bindermaterials with solid properties, ricin, Bacillus anthracis, botulintoxin, Francisella tularensis.

Environmental pollutants may also be processed using these methods andapparatus including, but not limited to, pollen, mold spores, bacteria,cement dust, fly ash, oil smoke particles, tobacco smoke particles,soot, and carbon black.

The particles may also be selected, without limitation, from narcotics,pharmaceuticals; cosmetics; cement materials; components used in inks;food substances including sugar and flour; cosmic or “space” dust, andother particulate matter derived from comets, asteroids, meteroids;contaminants of any of the materials described in this application; andany other compositions that are supplied or may be detected in powder orparticulate form.

In accordance with other aspects of the invention, the particles used inthe sieving and dust storm techniques are preferably solid (i.e., have afixed shape and volume). Although the particles deposited by dust stormare not particularly limited, they preferably range in size from about 1to about 100 microns, preferably from about 3 to about 50 microns, andmore preferably from about 5 to about 30 microns. Preferably, theparticles do not exhibit significant levels of clumping or agglomeration(i.e., less than about 50% of the particles are clumped/agglomerated,preferably less than about 25%, more preferably less than about 10%, andstill more preferably less than about 5%), which in some aspects may berelated to the moisture content of the particles. The particles may havea moisture content that is less than about 25% by weight, preferablyless than about 10% by weight, more preferably less than 5% by weight.In some aspects, the moisture content is approximately 0% by weight, andmay be achieved by any drying technique that does not alter the shape orsize of the particles.

The ideal particle size and shape is determined by the application andthe need to fabricate representative samples with corresponding particlesizes and spatial coverage. For security applications which relate todepositions of particles within fingerprints, a range of particle sizesare crushed and deposited with a typical range (comprising 75% of theparticle mass) being from 1-25 microns in diameter. To avoid particleaggregation in the sieve pan, dry particles and a dry atmosphere ispreferred. As the size of the desired particles decreases it becomesincreasingly difficult to sieve through smaller sieve meshes. This isparticularly marked for sieve meshes with openings with dimensions lessthan 10 microns. The dust storm technique is not restricted by any sievemesh opening size and may be applied to any size range of interestbetween 1-100 microns.

In accordance with the invention, coupons or test coupons are substrateshaving surfaces designed to receive the distributed particles thereon,and may be provided in any shape or size desired. For example, squarecoupons that are 1″ by 1″ are preferred in some aspects of theinvention. The coupons are preferably formed from a material thatexhibits little or no reactivity with the deposited particles. In someaspects, it is permissible for the substrate to interfere with thefunctioning of the detection equipment that may be used to detect thedeposited particles, in which case the detection equipment separatessignals from the target analyte from signals from the substrate, forexample, using an algorithm. Exemplary materials for use as test couponsinclude glasses used in consumer electronics or automobile applications.Silicate glasses, such as soda lime glass and borosilicate glass, may beused. A wide range of polymers may also be used in accordance with theinvention, such as polymethacrylate, polystyrene, Bakelite,polyvinylchloride, nylon, polyethylene terephthalate, polyurethane,polycarbonate, or polyethylene. Metals, painted metals, wood, paper,cardboard, and woven cloth may also be used as test coupons.

In one embodiment, the test coupon material is formed from a substratematerial that exhibits minimal or no reactivity with the particlesdeposited thereon. However, in other embodiments it may be desirable forthe particles to interact with the surface of the coupon or substrate,for example, to cause the deposited particles to adhere to the surfacewith the characteristic forces or bonding present, including but notlimited to covalent bonding, ionic bonding, hydrogen bonding, Van derWaals forces, and capillary action of a co-located liquid such as sebumoil. A cover slip may optionally be applied to the particles depositedon the test slip in some aspects of the invention.

An adhesive layer can optionally be applied to the surface of the testcoupon and/or a slide cover can be placed on the surface of the couponafter the particles have been deposited therein in accordance with someaspects of the invention. Preferably the adhesive does not alter theproperties of the deposited particle, or interfere with the functioningof a detection apparatus used to detect the presence of the depositedparticle.

In some aspects of the invention where improving the accuracy ofdetection of particulate matter in fingerprints or other body parts isimportant, it may be beneficial to apply a pattern of sebum oil and/orsweat to the coupon prior to or after depositing the particulates. FIG.17C is a photomicrograph that shows RDX particles deposited onto asubstrate containing pools of sebum oil. The sebum and/or sweat may beapplied as a layer, or in a manner that mimics contact of a body partwith the coupon, for example, full or partial prints deposited bycontact with the hands or fingers. The sebum and/or sweat may bedeposited by touching the coupon with a body part of interest, orsimulated version of a body part, or by using a printing technique thatapplies background compounds typically found on the body part ofinterest (i.e., in the case of contact with skin, applying one or moreof glycerides, fatty acids, wax esters, squalene, and sterol estersfound in sebum; and/or applying one or more of amino acids, proteins,urea, uric acid, lactic acid, sugars, creatinine, and choline found insweat) that are likely to be present along with the particulate matterbeing detected. When improving the detection of particulate matter inother deposited background materials is important, conditions may bereproduced using the mechanism responsible for deposition (i.e., bytouching the coupon with a finger), or printing techniques using thelikely background compositions can be employed. Non-limiting examplesmay include, without limitation, footprints, tire tracks, respiration,and detection in hair or fibers from clothing. Background compositionslikely to be present as a result of these types of contact can bedetermined using available forensic reference materials.

Regardless of whether sieving, dust storm, or particle printingtechniques are used for particle deposition, it is an aim of theinvention to provide feedback control during the sieving, dust storm, orprinting process to halt particle deposition when a desired targetloading has been achieved. Such feedback control may be accomplished byusing optical sensors, weight sensors, or any other type of sensorcapable of detecting the presence of particles on the coupon(s) andtransmitting the information to a controller or processor used tomonitor the particle deposition.

Further, it is the aim of the invention to allow smaller particles ofinterest to be deposited and fractionated (for example, particlesranging in size from 0 to 10 microns, 5 to 15 microns, 10 to 20 micronsor 0 to 20 microns) in a dry atmosphere, which may aid in preventingparticles from aggregating prior to deposition, or absorbing water ifthey are deliquescent, which may cause them to dissolve or otherwise nolonger be in a solid form. The dry air supply conditions the air insidethe sieving stack or dust storm apparatus, or in the environment whereparticle printing occurs. This permits more efficient deposition ofparticles, particularly for particles having dimensions of less than 20microns, and generally improves sieving control for all particulatematerials. For hydrophilic or hygroscopic materials, dry airconditioning within the sieving stack or dust storm apparatus, or in theenvironment of the particle printing apparatus, is particularlybeneficial. The dry atmosphere may have a relative humidity of less than30% at the temperature being used to process the particles. Preferably,the atmosphere has a relative humidity of less than 20%, more preferablyless than 15%, most preferably less than 10%. In some aspects, theatmosphere has less than 5% relative humidity at the temperature beingused to process the particles, preferably approximately 0% relativehumidity. In order to accomplish this level of dryness, the containerused to hold the material being sieved or subjected to a dust storm orprinted may be equipped with a valve to permit dry air to be fed intothe container volume, and optionally the container may be equipped witha desiccant material to aid in absorbing any residual water vaporpresent in the container or contributed by the particulate material.

The air to be introduced into the sieving or dust storm apparatus mayhave a specific temperature, where the temperature may be selected sothat the particles of interest remain solid and/or non-reactive and theeffects of any residual moisture are limited. Room temperature air ispreferred in some aspects of the invention, but it is also envisionedthat certain particles may benefit from the use of chilled or heatedair. The air temperature may be selected based on the particles ofinterest, and may be adjusted to ensure that the particles remain solidand non-reactive, or to cause them to become more reactive.

The sieving and dust storm deposition techniques of the inventiondeposit particles in a random fashion. Therefore, the amount ofdeposited particles on two sample coupons (or different areas of thesame coupon) cannot be exactly the same. The terms “uniform,” “similar,”“comparable,” and “reproducible,” when used with respect to the particledeposition achieved by the apparatus and methods of the invention shouldbe interpreted to mean that the difference between the amount ofparticles deposited on a first sample coupon and a second sample couponis within the values expected by statistics.

The number of particles randomly deposited in a given area is governedby the Poisson distribution. The probability that a given number ofparticles will be deposited in a given area is:

${p(N)} = {e^{- {\langle N\rangle}}\frac{{\langle N\rangle}^{k}}{k!}}$

where <N> is the average number of particles expected to be deposited.

The average number of particles expected to be deposited is determinedby the average mass loading, area of sample, and average particle mass:

${\langle N\rangle} = \frac{\mu \; A}{\langle m\rangle}$

For example, if the average number of particles in a given area is only1, there is a ˜37% probability that the area will remain empty and a˜63% probability that the area will be populated with 1 or moreparticles. The resulting Poisson distributions when the average numberof particles in a given area is 1, 4, or 10 are shown in FIG. 1. Byincreasing the observation area (for the same areal mass loading), thisvariation decreases.

For larger numbers of particles, the average variation in the number ofparticles in a given area can be best described by the square root ofthe variance of the Poisson distribution, which can then be interpretedas the standard deviation of an equivalent normal distribution:

σ≈√{square root over (Var(P))}=

In this case, we can state that there is 68.3% probability that theobserved (deposited) number of particles is in the range:

N

−

<N _(observed) <

N

+

It is important to note that as the number of particles grows, therelative deviation in the number of deposited particles decreases and isgiven by:

1/

Any deposition that has a deviation in particle numbers between twoareas that is (substantially) greater than given by the above twoequations can be considered to be “non-uniform,” “not reproducible,”“dissimilar,” or “not comparable.” The sieving and dust storm apparatusof the invention may be beneficially used to avoid non-uniform particledeposition.

When the terms “uniform distribution” and “substantially uniformdistribution” are used in accordance with the various embodiments of theinvention, it is understood that for areal densities of particlesranging from 0.01 to 200 micrograms/cm′ provided on the coupon orsubstrate in the desired areas as a result of using the apparatus andmethods of the invention, the areal density on average varies by lessthan 100% in the target region coated. Preferably, the particle arealdensity varies by less than 50% in the target region coated. Morepreferably, the particle loading areal density varies by less than 10%in the target region coated. Most preferably, the particle loading arealdensity varies by less than 3% in the target region coated. The loadingmay be non-uniform in accordance with some embodiments of the invention,for example, a particular desired particle loading may be achieved in asmaller target area within the deposition surface area by use of a maskor other means for limiting particle deposition to a target area, wherethe remaining surface area outside the target area contains noparticles. It is understood that the desired areal density and aerialdensity uniformity of the particles varies depending on the relevantapplication and the particle type being deposited, and the nature of thefurther analysis to be conducted using the particles. For example, inorder to fabricate test coupons to mimic particles deposited in afingerprint it is desirable to control particle depositions in aheterogeneous fashion with small islands of particles with relativelyhigh areal densities.

One preferred embodiment of the invention deposits small solid particlesthrough a sieve, or using a dust storm technique, or by direct particleprinting, onto one or more coupons in a controlled fashion in order toproduce a reproducible average distribution of particles on each couponin a targeted area. One or more test coupons may be monitored as a wayof assessing the particle loading over multiple coupons which are notmonitored.

The particle-deposition apparatus and techniques of the inventioncorrect for particle deposition non-uniformities by moving the couponsduring particle deposition, randomizing particle movement, or directingdeposition on a particle-by-particle basis, thereby avoiding exposure tonon-uniform deposition conditions. The invention also expands the rangeof particle sizes that can be uniformly deposited, and in particularallows practical depositions of particles in the 5-20 micron size rangewhen using sieves with comparably-sized openings. These aims of theinvention are of particular importance for fabricating test specimens tobe used in analytical applications such as trace particle detection ofexplosives, narcotics, or of other environmental pollutants. Theinvention may also find applications in formulating or processingpharmaceuticals, cosmetic products, cement materials, inks, andfoodstuffs.

Various apparatus suitable for use in carrying out the invention willnow be described in connection with the drawings provided herein. Theinvention will also be described with respect to presently-preferred andexemplary methods for employing the apparatus described herein. Theapparatus described herein are not to be construed as limited to use inany particular methods, and the methods are not to be construed aslimited to any particular apparatus, and neither are to be construed aslimited to the detection of any particular particles or substrates ofinterest. It is to be understood that the various embodiments discussedbelow are not intended to be limiting, and that alternativeconfigurations and techniques are envisioned based on these exemplaryapparatus and methods that achieve the desired particle processing.

Sieving

The sieving apparatus and techniques in accordance with the inventionmay preferably be based on a vibration generator that generatesvibrations, such as a shaker apparatus. The vibration generators of theinvention include, but are not limited to, shakers such as the GilsonPerformer III sieve shaker platform (manufactured by the Gilson Company,Inc., of Lewis Center, Ohio). Shakers may incorporate electromagneticvibratory action with amplitude and timer control, and optionallyprovide impact hammer tapping action to reduce clogs in the sieve mesh.

An outside view of a sieving stack 1000 that may be used to achieveparticle sieving is illustrated in FIG. 2. The sieving stack 1000includes an upper lid 1100 that covers a sieving pan 1200. The sievingpan 1200 sits above a collection pan 1300, which may include a substrateholder 1400 therein. The substrate holder may include a mask 1410, asubstrate upon which particles are to be deposited 1420, and a substrateholder or platform 1430.

Additional variations in sieving stacks in accordance with the inventionare illustrated in FIGS. 3-9.

FIGS. 3A and 3B depict embodiments of a preferred sieving apparatus inaccordance with the invention. In FIG. 3A, a shaker apparatus 1800 isdepicted with a sieve stack 1000 affixed thereto. Shaker 1810 includes avibration plate 1820 thereon, and the vibration plate 1820 includessupport rods 1830 that extend up in order to securely support the sievestack 1000 and transmit vibration throughout, as well as permit astriker plate 1840 and striker 1850 to be mounted above the sieve stack.The striker plate 1840 may be impacted by the striker 1850 duringsieving to prevent sieve blockages and irregularities in particledistribution from occurring. The sieving stack includes lid 1100 havingan optional air inlet port 1600 provided therein (in some aspects, suchas the one depicted in FIG. 3B, the air inlet port 1600 may be providedin the side wall of the sieving pan). Sieving pan 1200 includes asieving membrane or mesh 1210, and may also include a wiper or blade1220. When wiper 1220 is provided, a motor 1500 may be provided to driverotation of the wiper 1220 over sieve membrane 1210, further improvingthe distribution of particles across the surface of the sieve andspeeding sieving time.

Any particles that are able to pass through the sieve fall intocollection pan 1300, which holds substrate/coupon holder 1400. Thecoupon holder 1400 has a mask 1410 provided on an upper surface thereof,which exposes only the portion of the coupon 1420 upon which particlesare to be deposited. The coupons 1420 are placed in a coupon platform1430 that may be outfitted with a vibration damper 1440. The couponholder 1400 may be configured to rotate in order to preventirregularities in particle deposition across the coupons 1420, and arotating coupon holder 1402 is shown in FIG. 3B. All motors andactuators used in the sieving apparatus, as well as the shaker, may becontrolled using a controller 1700, which may be programmed to vary theintensity of shaking, the frequency of striking, the airflow, the speedand direction of rotation of the sieving blade, and the speed anddirection of rotation of the coupon platform. In some aspects, theprogrammed controller may adjust these or other variables based ondirect user input. In other aspects of the invention, the controlleradjusts variables based on detection of blockages on sieve membranes,and the weight and distribution of particles detected on one or morecoupons.

FIG. 3B depicts an extension sleeve 1310 incorporated between the sievepan 1200 and the collection pan 1300. When provided, the extensionsleeve 1310 provides additional clearance for the coupon holder 1400,which may be particularly useful when a rotating coupon platform 1402 isprovided to support the coupons 1420.

FIG. 4 is an exploded view of the elements of the sieving apparatus asshown in FIG. 3B.

Sieving stacks may be based on one or more sieving pans that arearranged by stacking them, and where more than one sieving pan isprovided, they are preferably stacked in order (from top to bottom) sothat the sieve with the mesh that permits the largest particles to passthrough is provided at the top, and the sieve with the mesh that permitsthe next largest particles to pass through is in the middle, and thesieve with the mesh that permits the smallest particles to pass throughis provided at the bottom. Such an arrangement may provide moreefficient sieving while avoiding clogged mesh. The one or more sievingpans are stacked on a collection pan, which captures the particles thatare able to fall through the sieve or sieves. Conventional orcommercially-available sieving stack components may be used inaccordance with the invention, incorporating one or more of themodifications described herein.

In some embodiments of the invention, the sieve may be formed using ametal mesh or fabric. Non-metallic mesh or membrane may also be used inaccordance with the invention, and such sieves may be formed, forexample, from polymers such as polyester or nylon. The mesh size of thesieve may range from 2500 mesh (5 microns) to 35 mesh (425 microns),preferably from 1250 mesh (10 microns) to 60 mesh (250 microns), morepreferably from 800 mesh (15 microns) to 60 mesh (250 microns), and mostpreferably from 625 mesh (20 microns) to 200 mesh (75 microns). In someaspects, it is preferred that the mesh size be selected to allow foreffective sieving of particles ranging from 1 to 20 microns in size,i.e., from 2500 mesh to 625 mesh. It is understood that sievingmembranes will permit particles corresponding to the given mesh size orsmaller to pass through the sieve for deposition onto the coupon orsubstrate. In some embodiments, in order to increase particleuniformity, the particles may be pre-screened one more times to removeparticles that are less than a designated size. Particles may also beground using a mortar and pestle (automated or not), or milled (forexample, using a ball mill) before being used in the sieving apparatusand methods of the invention. Such pre-deposition processing maybeneficially improve the consistency and size uniformity of thedeposited particles. The composition of the sieving membranes used inaccordance with the invention may be varied as long as they achieve thedesired level of sieving efficiency and uniformity of particledistribution.

Sieving Under Dry Conditions

Processing particles in a dry atmosphere generally reduces particleagglomeration in the sieving pan, allowing improved sieving particlethroughput via sieve openings and onto coupons positioned below thesieve. Sieving techniques including shaking the entire sieving stack andapplying periodic impulse strikes to the top of the stack using astriker may be employed to reduce agglomeration. It has been found thatthe use of dry air further improves particle processing, and may bepreferred where the particles are prone to agglomeration.

In order to provide a dry air supply to the sieve stack, the lid of thesieving stack or the side of a sieving pan may be modified to provide anattachment point for the dry air supply. Mounting the air valve on theside of the lid or sieving pan beneficially avoids direct airflow ontothe particles resting on the mesh of the sieve, thereby avoidingundesirable airflow redistribution of particles positioned on thesieving mesh. Various configurations for sieving stacks that include thedry air supply 1600 are shown in FIGS. 3A, 3B, and 4. (The use of dryair supply 1600 with attached air inlet tube 1610 is shown in FIG. 8.)

In some aspects, conditioning the air for zero humidity allows particlesieving through mesh sizes with openings of less than about 20 microns.Sieving with a 10 micron sized mesh under zero percent relative humidityis possible using this optional sieve stack modification. Sieving underzero percent relative humidity can be included as part of a standardprotocol in some embodiments. An initial preconditioning of particles inthe sieving pan(s) (“drying time”) is sometimes desirable prior to theinitiation of the actual sieving process in order to ensure that thematerial to be sieved is completely dry. For some materials, it is alsohelpful to precondition the particles under 0% relative humidity duringany procedures leading up to loading the sieve pan. This optional aspectof the invention can be achieved, for example, in a glove box with a dryatmosphere. To maintain the low or no humidity atmosphere, desiccantmaterials may be placed in the sieve stack in locations where they arenot likely to interfere with sieving or impact particle distribution,such as on the underside of the sieving pan lid, or on the side of thesieving or collection pans in a location that does not impede rotationof the sieving blade or rotating coupon platform, if provided.

Coupon Holder

To avoid contamination or agglomeration, it is desirable to catch thesieved particles as they fall through the lowest sieving pan before theycontact the collection pan. One or more glass coupons may be positionedin the collection pan to receive the particles. In one aspect of theinvention shown in FIG. 5, a coupon holder or substrate holder 1400 isprovided in a collection pan 1300, which may include an optional anextension sleeve 1310. The substrate holder 1400 keeps the one or morecoupons or collection substrates (not shown) in place during particledeposition.

Additional features may optionally be incorporated into thecoupon/substrate holder 1400, for example, to improve uniformity ofparticle deposition on the coupons. In some aspects, a mask 1410 isprovided to control the area of the coupon upon which particles may bedeposited. The coupon holder can incorporate a substrate platform 1430that incorporates recesses 1432 to house gaskets 1434 that mate to thecoupons in order to keep the coupons secure while sieving is performed,and to relieve any stresses applied to the coupons when the optionalcoupon mask 1410 is secured to the coupon holder. The recesses in thecoupon holder can be adapted to accommodate different coupon sizes orshapes.

It should be appreciated that different sieve sizes and different couponsizes may be selected so that a smaller or larger number of coupons canbe coated simultaneously. Coupon substrates may be provided in any size,but are preferably square, and more preferably are square withdimensions of 1 inch×1 inch. For a typical 3-inch diametercommercially-available sieve pan, this allows four coupons to besimultaneously coated during the sieving operation.

The main functionality of the coupon gasket 1434 is to gently press thecoupon against the mask 1410 and keep the coupon in position. By design,a coupon only contacts the gasket at its outer edges to limit anypossible contamination from the gasket (e.g. monomer or plasticizerbleed from the gasket). According to some aspects, a harder or moredense gasket (e.g., a gasket made from Dragon Skin® 20 silicone rubber,manufactured by Smooth-On, Inc., of Macungie, Pa.) may be easier toseparate from glass coupons than softer or less dense gaskets (e.g., agasket made from Ecoflex® 00-30 silicone rubber, manufactured bySmooth-On, Inc., of Macungie, Pa.).

In some embodiments, the coupons are covered with a mask in order tocontrol deposition of particles on the coupon surface. The mask designmay vary depending on the particular needs of the end user of thecoupons. In some aspects of the invention, the design of the couponholder provides the capability to select from multiple different maskshaving openings of different sizes and shapes (e.g., circles, ovals,squares, or rectangles of varying sizes), which are not limited inaccordance with the invention. One example of a mask 1410 havingcircular openings 1412 therein is shown in FIG. 5. In some aspects ofthe invention, the masks are made of metal. Other mask materials mayalso be used, such as plastics. The mask material is preferably selectedso that the mask is rigid enough not to bend while pushing against thecoupon, in order to prevent an air gap from appearing between the maskand coupon, which could lead to unwanted particle contamination beyondthe areas defined by the mask. The mask may also be designed to be asthin as is practical to avoid particle “shadowing” effects adjacent tothe lip of the mask. Although it may be possible in some aspects totaper the edges of the mask openings, it could be counterproductive incertain configurations if doing so permits particles to “roll” onto thecoupon and form agglomerations around the edges of the mask opening. Theopenings of the masks may be machined precisely enough to mount the maskin either orientation without regard to which side is the top and whichside is the bottom, and doing so would allow all each of the multiplecoupons to be coated in the same masked area as an individual coupon.

Once the coupons are positioned on the gaskets, or below the gaskets innotches in the coupon holder, the mask can be affixed to the top of thecoupon holder. Any means of attachment may be used in accordance withthe invention, such as screws or clamps (see, e.g., FIG. 5, screw 1414).

In one aspect of the invention, a small screw with a lock nut on top(see, e.g., FIG. 4, nut 1416) may optionally be included to enable easyinsertion and extraction of the coupon holder from the receiving orcollection pan 1300. The coupon assembly may be affixed to the floor ofthe collection pan 1320 using vibration dampers 1440 that sit inrecesses 1360 configured to hold dampers 1440, as shown in FIGS. 5 and6. This feature helps to maintain alignment of the coupon assembly withrespect to the rest of the sieving apparatus, and helps to preventunintended contact between the wall of the collection pan and therotating coupon assembly.

The insertion and positioning of the coupon holder in the sieving stackis typically a manual procedure, though automatic means may also be usedin accordance with some aspects of the invention. Positioning the couponholder requires care to ensure the coupon holder does not make contactwith the wall of the receiving pan while operating the sieve stack inorder to avoid transmitting vibration to the coupons and impactingparticle distribution thereon. To simplify the coupon holder insertioninto the receiving pan, a ring (not shown) could be used to align theholder within the pan. The inner diameter of such a ring should be largeenough to match the diameter of the mask or coupon holder (whichever islarger), and the outer diameter should be small enough to fit into thereceiving pan.

In embodiments where the mask is used, the surface area of the sieve islarger than the surface area of the masked area(s) on the coupon(s),which leads to losses of particles during the sieving process. Thismaterial may be captured in the collection pan, and if necessary thismaterial can be reclaimed after the sieving is completed.

One or more test coupons used in accordance with the invention may beheld in a stationary position in order to allow particles from thesieving apparatus to be deposited thereon. However, in a particledeposition environment with particle flux discontinuities, an unevendistribution across the collection pan or coupons positioned in thecollection pan can result if the coupon platform is stationary. Tocounter this issue, several optional modifications to the couponplatform may be employed individually or collectively in order to assistin averaging or evening out particle deposition patterns.

Rotating Coupon Platform

In one alternative, the one or more test coupons may be held on a movingcoupon platform in order to compensate for any lack of uniformity indepositing particles during the sieving process. Preferably, the movingplatform is a rotating platform. The rotation may be generated, forexample, by using a windable spring-based mechanism, or a motor. Thespeed of the moving platform may be controlled manually, or by using amicrocontroller attached to the motor. The microcontroller may beprogrammed to permit a user to vary the rotation speed. Alternatively,the microcontroller may be programmed so that the rotation speed isadjusted automatically based on information regarding the particles(such as density and size), the detection of particle fluxnon-uniformities, and the loading level of the coupon or coupons,beneficially permitting end result-controlled test coupon fabricationthat achieves specific desired particle size and areal coverageparameters.

For example, with respect to the coupon platform shown in FIG. 5, inwhich a 3-inch diameter circular collection pan 1300 houses an array offour 1 inch square coupons arranged on a coupon holder 1400, a motorizedstage 1430 is provided. The coupon holder 1400 may be rotated around acentral axis A with a fixed distance between a coupon and the axis ofrotation. In other embodiments, a rotating coupon platform may be usedwhere the radius representing the distance between the coupon and theaxis of rotation is varied during sieving operations (not shown),further improving system performance with respect to averaging particleflux from the sieve pan to collection pan.

The rotation of the coupon array platform should be fast enough to avoidparticle aggregation due to particle flux discontinuities, typicallysubstantially faster than the rotating blade sieving operation, withspeeds of 2 to 10 times faster being typical, but not so fast as tocause excessive particle roll when a particle lands on a coupon (drivenby centripetal forces) or particle redistribution after surfaceattachment (or complete detachment) towards the circumference of thecollection pan. The rotating coupon platform permits improved particledeposition uniformity, and reproducibility of particle deposition ondifferent coupons. Optimization of rotation speeds and forwards andbackwards timed cycles may further improve particle depositionuniformity on loaded coupons.

In one aspect of the invention shown in FIG. 5, an electrical conduithole 1350 in the sidewall 1330 of the collection pan 1300 providesaccess for any electrical cabling to power or control the motor. A plugor patch (not shown) may be formed, for example, using tape, epoxy, orany suitable sealing material, and can be used to block any remaininghole not filled by the wires in order to prevent airflow from beingchanneled through the hole. Another optional location for a conduit hole1350 is shown in FIG. 6, in which the conduit is provided through thebottom of the collection pan.

As shown in FIGS. 3A, 3B, and 4, a microcontroller 1700 and one or morestepper motors 1500 may be used to control the motor and rotating couponplatform. One exemplary microcontroller that may be used in accordancewith the invention is the Arduino® microcontroller from AdafruitIndustries, New York, N.Y., though the invention is not limited to anyparticular microcontrollers or associated software. In-house developedfirmware allowed for control of rotating coupon platform functionsincluding: rotation velocity, rotation time duration, rotationdirection, continuous or alternating direction of rotation, radius ofcoupon rotation, and timing synchronization with the Gilson Performer®III3 sieve shaker unit (including both vibration and periodic striking).It will be appreciated that any general purpose controller may be used,and that the controller may be programmed to carry out these or otherrotating coupon platform functions.

The height of the coupon assembly and the motorized stage that providesrotation of the coupon assembly may be higher thancommercially-available 3-inch diameter collection pans, as shown inFIGS. 3B and 5. In order to connect the collection pan and couponassembly to the sieving pan, an optional sleeve 1310 may be used to matethe two pans together while allowing sufficient head room below thesieving pan to accommodate the motorized coupon assembly.

Vibration-Isolated Coupon Holder

One challenge with employing a commercial sieving stack system and thefabrication of an array of particle-coated coupons is the vibrationcoupling of the sieving stack to the coupons themselves. This can leadto undesirable particle redistribution on the coupons after theirinitial deposition on a coupon. In some aspects of the invention, thiseffect may be eliminated or significantly reduced by physicallydecoupling or isolating the coupon from the collection pan vibrationsource and/or isolating vibration of the coupons.

Vibration isolation may be achieved according to one aspect of theinvention by using an assembly with viscoelastic rubber or foam mountsthat form an interface between the collection pan and the couponassembly. Exemplary mounts are shown in FIGS. 4 and 5, as feet 1442.

According to one aspect of the invention shown in FIG. 6, the couponholder (not shown) may be decoupled from the vibrating collection pan byproviding a conduit hole 1350 in the bottom surface 1320 of thecollection pan 1300 (if required for power). This may be achievedthrough electromechanical decoupling or mechanical decoupling.

The mechanical decoupling may be accomplished using damping, which canbe achieved by one or more means including, but not limited to: springs,ball bearings, viscoelastic polymers, and/or foam spacers. Thesedecoupling means all employ the physical property of inertia. As shownin FIGS. 4 and 5, one technique for decoupling vibrations sourced fromthe receiving pan 1300 to the coupon holder/assembly (not shown) is touse a viscoelastic rubber material to absorb and dissipate themechanical vibration energy. Coupon holder base 1450 is provided at thebottom surface 1320 of receiving pan 1300, and vibration damper 1440 isformed using multiple rubber feet. The damping accomplished using thisapproach is maximized when the viscoelastic properties of the rubbermaterial are a suitable match for the vibration frequencies involved. Itshould be noted that low frequency vibrations are much less likely todisplace small particles, as compared to high-frequency vibrations.Accordingly, complete mechanical decoupling is often not necessary inorder to use the sieving apparatus of the invention, and carry out thesieving methods of the invention.

FIG. 7 depicts an aspect of the invention in which an electromechanicaldecoupler 1444 is used to dampen vibrations received through base 1450so that they are not transferred to substrate platform 1430, whichsupports the coupons (not shown) and receives mask 1410. Using theelectromechanical decoupling approach shown in FIG. 7, the underlyingidea is to employ an inertial instrument 1444 that is provided betweencoupon holder base 1450 and coupon platform 1430 to measure inducedmovements in the collection pan, and produce a counter movement in thecoupon holder to cancel out collection pan-induced movements in thecoupon assembly. This approach delivers optimum decoupling results, butis more complicated to implement than a mechanical decoupling approach,especially in view of the compact designs preferred in some aspects ofthe invention. Comparable systems can be found in stabilization systemsfor digital cameras or in optical tables. One advantage of amicroprocessor-controlled electromechanically decoupled coupon holder isthe ability to adapt to different frequencies from a vibration source inreal time.

As shown in FIG. 8, vibration isolation may be achieved by separatelysupporting substrate holder 1400 so that it does not contact collectionpan 1300 or sieve pan 1200. This may be accomplished, for example, byaffixing the coupon holder to a metal rod 1900 which may be mountedusing a clamp 1910 to a fixed support 1920 (such as a ring stand, thoughother apparatus for providing a secure mount may be provided). The armor rod 1900 passes from outside the sieving stack into the collectionpan 1300 through a hole 1340 in its side wall 1330 without contactingany part of the sieving stack 1000. To keep the hole in the receivingpan 1340 as small as possible, the rod may be removed to place thecoupon holder 1400 in the pan 1300, and then the rod 1900 may beattached to the coupon holder 1400, preferably at its base 1450. Inorder to maximize the effectiveness of this configuration, the couponholder 1400 should be completely level, and the rod 1900 should notcontact the edge of the receiving pan 1300. The rod may be supported,for example, by a ring stand 1920, although in some aspects the rodsupport is a heavy support, or a support that is separate from thesupport for the sieve shaker, in order to reduce the impact of vibrationtransmission through the support surface itself.

Electrically Grounded and Suspended Coupon Holder

Another possible source for non-uniform particle coverage on coatedcoupons may stem from electrostatic charging of various sieving stackparts. Resulting electrical fields may force the particles to adopt aflight path from the sieving to collection pan which differs from anatural gravitational fall. To avoid undesirable charging, in someaspects of the invention the sieving assembly may be grounded for allelectrically-conductive parts. (See, for example, grounding wire 1822 inFIG. 8 provided on shaker vibration plate 1820.) Such grounding, whenused, may also be provided to ground the sieve stack with the sieve andpan, the sieve shaker housing, the ring stand and metal rod (if used),as well as the metal mask used to pattern the particle deposition on thecoupons.

Wiper Mechanism

In some aspects, suspending or decoupling the coupon holder from thesieve shaker, or providing a rotating coupon platform greatly improvesthe control of the sieving process and the ability to deposit a uniformdistribution of particles. However, even when the coupon holder isdecoupled from the sieve shaker, or rotates to minimize flux, adegradation in the uniformity of deposited particles can be observedover long durations of sieving (e.g., sieving that occurs over a periodof 5-10 minutes or greater). By observing the raw material loaded withinthe sieving pan (for example, by using a transparent sieving lid, or oneor more fiber optic cameras placed inside the sieving pans of thesieving stack), it can be seen that certain areas on the sieve maycollect a high concentration of particles while other areas have novisible particles, even when the sieving pan is level. This unevendistribution of particles across the surface of the sieve can lead to apoor uniformity of particles deposited on the coupons. At low loadingsin the sieving pan (i.e., loadings that do not cover the surface of thesieve membrane), nodal systems which may develop in the sieving membranecould be the source of this uneven distribution.

Another challenge associated with conventional vibration-driven sievingis the time taken to deposit particles having a size in the range of5-20 microns through a membrane with 20 micron openings. Depending onthe target particle loading on a coupon, the sieving process can takefrom several minutes up to several hours. In order to accelerate thisprocess and improve the distribution of particles within a sieving pan,a blade or brush may be rotated over the sieving membrane, and mayoptionally directly contact the sieving membrane. The rotating blade orbrush improves the average distribution of particles in the sieving pan,and thus improves the uniformity of distribution of the depositedparticles in the collection pan.

The use of the wiper is designed to address these issues, and mayprovide additional benefits. The sieve wiper may facilitate distributingor spreading the raw particulate material within the sieving pan. Thesieve wiper may also force particles, with minimal abrasion, through thesieving mesh. In doing so, the wiper maintains unblocked sievingmembrane holes, or unblocking holes which may have become blocked byparticles. When coupled with an air valve and source of dry air, thewiper may assist in providing a zero humidity environment within thesieve stack to reduce particle agglomeration and ease sieving forsmaller (<20 microns) particles at relevant mesh sizes by distributingthe dry air throughout the particles while agitating them to permit theair to permeate through the mass of material being sieved. The use ofthe wiper may simplify design and mechanical considerations for thesieving stack, and simplify maintenance functions such as assembly,operation, and cleaning.

The wiper may be operated so as to provide automated wiper control,including speed, duration, and direction control. The wiper assemblyprovided in accordance with the invention incorporates wiper bladematerials that avoid damage to the sieving membrane/mesh.

When a sieving technique is used for particle deposition in accordancewith the invention, it is an aim of the invention to speed up theparticle deposition process when sieving by employing a continuousblade, a segmented blade, or a brush that contacts the surface of thesieving membrane or the layer of particles provided thereon, improvingsieving uniformity by increasing contact between the particles and thesieve, and reducing clogging of pores in the sieve. The blade, segmentedblade, or brush in accordance with the invention may refer to structuresthat are formed of any materials that do not react with or damage thesieve or the particles of material being sieved. These materialsinclude, but are not limited to, rubber or silicone blades, and naturalor synthetic bristles.

Examples of blade configurations are shown in FIGS. 9A-9C. In FIG. 9A, arotating wiper 1220 is shown with the blade portion 1222 affixed to ablade housing or arm 1226, which is in turn affixed to a spindle or rod1228 that is adapted to be rotated (for example, by stepper motor 1500,shown in FIGS. 2B and 3). FIG. 9B shows a rotating wiper 1220 in whichblade 1222 incorporates several segments, notches, or gaps 1221 therein,to impart additional flexibility to the blade as it passes over theparticulate material and sieve screen. FIG. 9C depicts an aspect inwhich the blade is replaced with a brush 1224. Preferably, the blade,segmented blade, arm, or brush rotates over the surface of sieve, andtherefore is provided on a rod 1228 that is affixed to a motor or othermeans for rotating, where the rotation speed may be controlled by auser, or by a processor that determines the rotation speed based on userinput parameters or based on feedback regarding particle flux, rates ofparticle throughput, and/or particle loading on the coupons.

The wiper blade construct in accordance with this aspect of theinvention was fabricated in two main pieces, including a wiper basesupport 1226, 1228 assembled onto a stepper motor shaft (not shown), andinterchangeable blades, segmented blades, or brushes that are attachedto the wiper base. The interchangeable blades may be fabricated from arubber material. The design positions the edge of the blade in intimatecontact with the sieving membrane/mesh. The blade material should beselected to be soft enough to avoid damaging the sieve, but also stiffenough to push the particles across the surface of the sieve. Onepurpose of the wiper is to spread the particulate material around thesieving membrane/mesh to avoid particulates pooling in one area. Thewiper may also accelerate or force particulates through the openings ofthe sieve. In FIG. 9A, the blade can be seen to actually consist of twoseparate pieces 1222, which may be formed of rubber, although a onepiece blade is also envisioned in accordance with the invention. Theoptional blade separation is beneficial because it allows differentblade pieces to flex and bend in opposite directions while rotating orswitching directions.

To improve the sieving mechanism and maintain blade contact with thesieving membrane surface, a blade having a thin or sharp edge 1223 ispreferred, as shown, for example, in FIG. 9A. The blade preferablyretains sufficient rigidity to spread the particles across the sievesurface and force them through the sieve membrane. Its design retainssufficient flexibility to allow it to adapt to the surface morphology ofthe sieving membrane. This ensures that all the particulate material inthe sieving pan is continuously moved during sieving, and avoidsparticle pooling.

The lid of the sieving pan can be modified so that a motor is positionedon top of it. In this aspect of the invention, the shaft of the motorreaches through the lid into the sieving pan and the wiper blade isattached to the end of the shaft. The lid may also be modified to attacha dry air supply (see FIG. 3A, 1600). The connection between the wiperand the shaft of the stepper motor is height-adjustable, and allows forblade-sieving membrane clearance optimization. A transparent sieving panlid 1100 may optionally be provided to permit direct viewing of the 1200sieve pan to assess whether wiper blade adjustment is required. Thetransparent lid is preferably formed from a plastic material, though aglass lid is also envisioned.

The rotation of the wiper may be generated, for example, by using awindable spring-based mechanism, or a motor. The motor is preferably astepper motor, having a housing that is preferably rigid, and can beclamped to the sieve stack assembly 1000, as shown in FIGS. 3A and 3B,1500. It will typically not be necessary to build an extra housing toprotect the motor from clamping forces or impact hammer tapping, thoughsuch additional features are within the scope of the sieving apparatusof the invention.

The lid with the stepper motor, wiper/blade/brush, and dry air supply isshown in FIG. 3A. The wiper mechanism 1220 is shown installed on top ofa sieving pan 1200, which itself is mated to a collection pan 1300 withthe coupon holder 1400 positioned inside it. The attached stepper motorcontroller is provided on top of lid 1100. The controller 1700 can alsooptionally control the rotation of the rotating coupon holder 1430, whenprovided.

A microcontroller may be used to control the motor and blade/brush. Oneexemplary microcontroller that may be used in accordance with theinvention is the Arduino® microcontroller from Adafruit Industries, NewYork, N.Y., though the invention is not limited to any particularmicrocontrollers or associated software. In-house developed firmwareallowed for control of various blade or brush functions including:rotation speed, rotation time duration, rotation direction, continuousor alternating direction motions, and timing synchronization with theGilson Performer® III3 sieve shaker unit. Additionally, themicrocontroller is able to control rotations in certain patterns, forexample, by switching the rotation direction after every 2 fullrotations of the wiper. Rotation direction may also be adjusted based ontime, sensed particle deposition, or other factors input by a sensor orother device. It will be appreciated that a general purpose controllermay be used, and that the controller may optionally be programmed tocarry out these or other blade or brush functions.

In some aspects of the invention, the stepper motor controller isseparate from the controller for the sieving stack shaker, but it isenvisioned that the same controller can be used to control all sievingapparatus functions. The use of a single controller may beneficiallyallow synchronization of operations.

The complete sieving stack assembly is compact and easy to handle. Theindividual parts are simple to assemble and disassemble. Minor or noadjustments are required to position the blade after an initialadjustment is made to establish its contact with the sieving membranesurface.

As a result of these sieving operation design improvements achieved bythe apparatus and methods of the invention, the following improvementscan be realized: dramatically (>10×) decreased sieving time duration toachieve a target areal loading; and significantly improved uniformity ofdeposited particles over the coupons contained in the collection pan,and across the width of the collection pan. The time saving is believedto be primarily due to the wiper blade action which drives particlesthrough the sieving membrane or mesh. The wiper blade spreads particlesin the sieve pan across the sieve membrane and distributes them in amore uniform (average) fashion across the sieving membrane surface. Theuniformity of the deposited particles is a direct function of thisenhancement.

As a general comment regarding the sieving membrane design used inconjunction with a wiper assembly, a non-woven flat mesh or membranedesign is preferred. For a sieving membrane fabricated with a woven wiredesign, the membrane is inherently an uneven surface. In this case,because the blade only swipes over the higher points of the mesh, thisincreases the possibility of particles blocking holes. A brush designmay help in this regard. Fibers with a diameter comparable with the meshopening sizes maybe particularly useful in clearing any blockages. Evenif the sieving mesh or membrane is flat, it still may be difficult toensure contiguous contact of the blade with the sieving membrane so abrush assembly may be generally preferred over a solid blade,particularly for deposition of particulates that are more prone toaggregating and forming sieve blockages. A segmented rubber blade isalso envisioned as a possible solution to maintaining good contactbetween the blade and the sieving membrane.

In an additional aspect of the invention, the clogging of the sieve meshmay further be prevented by incorporating a series of ultrasonicactuators ringed around the exterior edge of the sieve pan and in linewith the sieving membrane (not shown). The actuators may be used inplace of a wiper assembly, or in addition to a wiper assembly. Uponactivation, the actuators may be used to dislodge the clogged particles.

Feedback Control

Another improvement described here are different feedback controlmechanisms to allow the sieving process to be automatically halted whena target loading has been reached. The sieving process is influenced byconsiderations including, but not limited to, the preprocessing ofparticulate material (manual or automated pre-grinding), the sievingmembrane structure (woven or non-woven mesh) and the blade or brushdesign.

In some embodiments, a window may be provided in collection pan 1300 toview the deposited particles, extension sleeve 1310 may be formed usinga transparent material, or a quartz crystal microbalance may be providedadjacent to the coupons in order to monitor particle deposition andprovide feedback control for the deposition procedure. When provided,the window or windows may preferably be formed in the bottom of the panto provide a direct view of at least one coupon. One or more windowsprovided in the side of the pan are also envisioned. An optical in situmeasurement or in situ miniature resonating device such as a quartzcrystal microbalance (QCM) or related surface acoustic wave (SAW) sensorcould provide the capability to halt the deposition process when adesired particle loading has been achieved on one or more of thecoupons. Because there is normally more than one coupon being coated,one or more coupons can serve as a witness coupon which is continuouslymonitored. This aspect of the invention can be particularly useful whenthe witness coupon is a glass microscope slide and the other coupons aresubstrates which are too rough to be considered for visible microscopycharacterization. Another approach could include a miniaturized digitalcamera unit with corresponding optics (for example, a magnifying lenssystem) embedded into the coupon holder base to allow direct monitoringof particles deposited by looking through a glass coupon during theparticle loading progress. Regardless of the mechanism used to detectthe particle loading, the deposition process may be halted, for example,by stopping the sieving of the particles (e.g., by turning off the wipermechanism or vibration generator), or by deploying a mask to preventdeposition of further particles on the coupons after a desired loadinghas been reached.

By incorporating one or more of a rotating coupon platform below thesieve in the collection pan, a wiper-assisted sieving procedure, and awindow or resonating device to observe depositions or provide feedbackcontrol in real time, the sieving apparatus and methods of the inventionbeneficially provide faster and more uniform deposition of particles ofinterest onto one or more coupons or test substrates.

Dust Storm

In other embodiments of the invention, the particles to be analyzed aredeposited by a dust storm apparatus and method as shown in FIGS. 10-11.The dust storm apparatus may incorporate a blower assembly, a fanassembly, or an acoustic transformer in order to create a particlecloud. It is understood that the speed at which the blower or fan isoperated, or the frequency at which the acoustic transformer isoperated, may be selected in order to cause particles of a certainweight and/or size to be dispersed within the atmosphere found in thecontainer. Other particles present in the container housing the blower,fan assembly, or acoustic transformer that are larger or heavier are notdispersed into the atmosphere of the container. In still otherembodiments of the invention, the particles to be analyzed may be sievedbefore being deposited by the dust storm technique. Alternatively, theparticles to be analyzed may be ground using a mortar and pestle(automated or not), or milled (for example, using a ball mill) beforebeing deposited by the dust storm technique. Such pre-deposition orpre-fractionation processing may beneficially improve the consistency ofthe particles deposited using the dust storm.

The dust storm deposition apparatus and methods of the invention permitfaster deposition of particles of interest in a controlled fashion toprovide a uniform distribution of a known or targeted amount of theparticles on one or more coupons or substrates. The invention providesreal-time feedback control over the particle deposition process,including the ability to halt deposition when a target loading has beenachieved. This has not been possible using existing sieving orinkjetting technology.

Dust storm deposition offers a rapid approach for loading a targetedamount of particles on a substrate. Uniform particle coverage ispossible under controlled conditions. However, a relatively largeparticle that will not stick on the coupon surface can knock off acluster of smaller particles to leave a bare patch of coupon.Prefractionation of the particulate material can eliminate undesirablelarge particles which are the source of this effect. For a glass couponsubstrate, in situ monitoring using a visible camera provides a path toprovide feedback control and turn off the dust storm when a targetedloading has been achieved. Alternately, a gravimetric device such as aquartz crystal microbalance (QCM) may be used to indirectly detect theweight of deposited particles on a coupon.

Exemplary particle milling apparatus are shown in FIGS. 10-12. Duststorm apparatus used to achieve particle distribution on a coupon inaccordance with the invention are illustrated in FIGS. 13-15.

Particle Pre-Processing

According to one aspect of the invention, the particles to be depositedusing the dust storm method and apparatus may optionally bepre-processed to more closely target the size distribution of theparticles for a particular application, and eliminate larger or smallerundesirable particles such that the desired particle size range is moreclosely achieved prior to initiating the dust storm. When the terms“uniform distribution” and “substantially uniform distribution” are usedin accordance with the various embodiments of the invention, it isunderstood that for areal densities of particles ranging from 0.01 to200 micrograms/cm′ provided on the coupon or substrate in the desiredareas as a result of using the apparatus and methods of the inventionthe areal density on average varies by less than 100% in the targetregion coated. Preferably, the particle areal density varies by lessthan 50% in the target region coated. More preferably, the particleloading areal density varies by less than 10% in the target regioncoated. Most preferably, the particle loading areal density varies byless than 3% in the target region coated. In some aspects, the particlesare milled until substantially all are within about +/−10% of the targetparticle size range extremities. It is understood that the desiredtarget particle sizes, range of particle sizes, and the amount ofparticles within a set of milled particles that meet the target or fallwithin a desired range may depend on a number of considerations. Theseconsiderations may vary, for example, depending on the particle beingdeposited using the dust storm technique, and the nature of the furtheranalysis to be conducted using the particles.

The pretreatment of particles prior to applying the dust stormtechnique(s) may be based on commercially-available milling apparatusdue to the more uniform particles produced, although manual techniquessuch as grinding of particles with a pestle and mortar may also be usedfor particle pre-processing in accordance with the invention. Millingapparatus suitable for use in the invention include apparatus suited fordry milling to produce fine particles, and may include ball mills, rotormills, mixer mills, planetary ball mills, jet mills, impact mills,mortar grinders, and jar mills. In some embodiments of the invention, astandard commercially-available ball mill machine can be used, andoptionally upgraded with a programmable power plug to time the millingand a dry atmosphere to perform the milling under. One example of a ballmill apparatus can be seen in FIG. 10, and includes a motor 2400provided on a base 2500 that is controlled using controller 2600. Motor2400 actuates a rolling component 2300 configured to rotate a canister2100 horizontally about its long axis.

Ball milling is a preferred technique in accordance with one aspect ofthe invention. Another view of an exemplary ball milling apparatus isshown in FIG. 11. The canister 2100 used for the ball milling mayincorporate metal sidewalls 2110, and be adapted to receive a lid (notshown). Steel ball bearings may be used as milling balls 2200, but ballsformed using other materials such as ceramic or rubber are alsosuitable. (In the case where explosive materials are being milled theuse of rubber balls or rubber coated balls may be preferred.) The amountof ball bearings may vary depending on the composition being milled. Theuse of too few bearings may result in pushing the material just ahead ofthe line of bearings, resulting in minimal milling. In one preferredaspect, the amount of balls loaded into the canister was sufficient tocover the entire floor or bottom of the can. The amount of ball bearingsused should be large enough to force the balls to tumble over each otherin order to produce the desired milling. The tumbling and the totalmass/weight of the milling balls enabled raw material grinding toparticles of the desired particle sizes.

The choice of material selected for the canister and milling ballsvaries, and the selection of these and other ball milling conditions arewithin the skill of those skilled in the art. For example, when both thecanister and ball bearings are made of steel, the texture present on theinner surface of the canister and the balls (particularly if combinedwith moisture in the air within the canister used for the ball millingapparatus), can result in most of the ground material sticking to theinner surface of the canister and the surfaces of the balls. However,even if most material is adhered to the ball milling apparatus, smallloose particles will also be present that can be used for laterdeposition on a coupon substrate using the dust storm approach. Thisobservation leads to the recommendation that very smooth millingcanisters and ball bearings may be preferred in order to reduce particleadhesion, or that a large amount of raw material be provided, or acombination of both, in order to optimize the efficiency of the ballmilling step when used in accordance with the invention.

A variation of the ball milling container is shown in FIG. 12, in whichcontainer 2100 is lined with metal strips 2120 that are attached to theinner wall 2110 of the container by clamps, suction cups, or otherattachment points 2122. As the ball grinding proceeds, particles aredeposited onto these strips. Afterwards, the container is disassembled,and particle-coated individual strips 2120 may be removed.

Milling can beneficially provide a more predictable range of particlesizes than a manually-operated mortar and pestle, or the use of the bulkcomposition prior to processing. If the variables including timeduration, can size, ball size, ball weight, number of balls, and theamount of raw material are controlled, the ball milling technique inparticular can be used to produce a predicable particle size range andamount.

Dust Storm Apparatus and Methods

In one aspect of the invention, the particles to be deposited on thecoupons are deposited using a dust storm. The dust storm techniquebeneficially results in a random distribution of particles on thesurface of a test coupon. A dust storm effect may be created using avariety of apparatus capable of causing particles to be dispersed intothe atmosphere in a manner such that they can be deposited onto one ormore test coupons. Non-limiting examples of apparatus that may be usedto generate a dust storm of particles include ultrasonic actuators andfans.

The dust storm apparatus and method incorporating an acoustictransformer may be operated at a frequency capable of generating a cloudof particles from a surface having particles deposited thereon. Thefrequency at which the acoustic transformer is operated may be adjustedin order to cause particles of a certain weight and/or size to bedispersed from the particle-bearing surface into an atmosphere. In someaspects, an acoustic transformer may be used to ultrasonically agitatean entire ball-milling container after particles have been milledtherein, causing particles deposited on the inner wall of the containerto be released.

The acoustic transformer allows for controlled release of particles froma substrate (e.g., a ball-milling container, a coupon, etc.) byadjusting the intensity or frequency of the ultrasonic waves. Thistechnique provides a distinct advantage in that it allows forpreferential deposition of a desired particle size by adjusting theultrasonic frequency. Without wishing to be bound by theory, it isbelieved that this is due to the fact that the adhesion force between aparticle and a substrate is proportional to the contact area of theparticle. At low ultrasonic intensity, only the large particles fall offof the substrate. As the intensity of the ultrasonic waves is increased,smaller and smaller particles begin to detach from the substrate.

In accordance with a method for ultrasonic particle deposition,particles larger than a desired size are removed first (whetherultrasonically or by other means), after which a sample coupon may beplaced under the substrate to collect the particle size or sizes ofinterest. Another advantage is that the sample coupon is free fromcontact with the particle source (unlike, for example, in a sievingstack where the sample coupon is enclosed inside the collection pan.)This allows more complex sample or coupon holders, including those withplanetary motions (for particle deposition uniformity), as well as thepossibility for in situ monitoring of the particle deposition process.For example, it would be possible to position the ultrasonic depositionapparatus and substrate above an inverted microscope positioned so as toview a glass witness coupon with the actual sample coupon next to itwhile the deposition container moves back and forth over the twocoupons.

As shown in FIG. 13, a strip coated with particulate matter may beinserted into an ultrasonic apparatus 2700 that may be controlled usingcontroller 2800. When a particle-coated strip 2120 is placed on theultrasonic apparatus 2700 and subjected to ultrasonic vibrations,particles 2121 are dislodged from the surface of the metal strip 2120and fall onto one or more test coupons or substrates 2710. The loadingof particles 2121 on the substrates 2710 may be controlled in someaspects by viewing the particle loading with an optical instrument 2900,such as a microscope. In this configuration, the ultrasonic source 2700,particle-coated strip 2120, and the coupons 2710 can beneficially beused without having to be provided within a container.

The fan-based dust storm apparatus and methods of the invention aredepicted in FIGS. 14 and 15.

As shown in FIG. 14, a fan apparatus 3400 is provided in a separatecontainer 3100 and suspended from container lid 3200 using wires 3300.When actuated, fan 3400 creates a dust storm by moving air in thedirections indicated by arrows in FIG. 14. Particles that have beenground using a ball mill or other grinding apparatus may be placed inthe dust storm apparatus for deposition onto one or more test coupons3510 housed in a coupon holder 3500, which may be positioned in the lid3200, or along the sides or bottom of the container 3100 (not shown). Insome embodiments, the container used for the grinding or milling may bedirectly affixed to the lid 3200 having the dust storm assembly attachedthereto. Unprocessed particulate matter may also be used in the duststorm apparatus, and the fan speed selected such that only smallerparticles will be dispersed into the atmosphere of the container fordeposition on test coupons.

In accordance with another aspect of the invention shown in FIG. 15, adust storm apparatus may be adapted for use directly with a ball millcontainer which has been used to grind particles. The ball millcontainer may be adapted to accept a fan-based blower system 3402 andsuspended from a ball mill container lid 3202 by suspension arms 3302. Acoupon platform 3502 may be positioned within the container, forexample, by affixing it to the wall 3112 of container 3102. The couponplatform 3502 may also be attached to the upper or lower surface of lid3202. In certain preferred aspects, the coupon platform is attached tothe upper surface of the lid 3202 and an aperture is provided in lid3202 (not shown) to serve as a mask, thereby allowing the particleswithin the container to be blown around in a random fashion anddeposited on one or more coupons secured to the lid of the container.

The fan-based dust storm apparatus described above may be implemented inorder to avoid the need to transfer particulate matter from the millingcontainer into a separate dust storm apparatus. The fan/blower is placedwithin the container by attaching the lid, preferably the couponplatform is provided opposite to the fan. The fan may be provided at thebottom of a container and the coupon platform may be provided on the lidof the container. Alternatively, the fan may be affixed to the lid ofthe container, and the coupon platform may be provided at the bottom ofthe container. The fan may be suspended within the container, and thecoupon platform may be provided at the top or bottom of the container.In other aspects, the fan may be provided on the bottom of the containeror on the lid of the container, and coupons may be affixed to the wallsof the container.

In some dust storm apparatus, the action of the fan may beneficiallyestablish cyclonic airflow within the container, causing the particlesto rotate around the inside of the container and be dispersed within theatmosphere of the container while continuing to rotate.

In order to break up possible agglomerations of particles beingsubjected to dust storm processing, lightweight beads may be included inthe container along with the particles. For example, polymer or plasticbeads may be used. Polyethylene (PE) beads are preferred in some aspectsof the invention, but any beads that are lightweight enough to flow withthe particles may be used, and beneficially permit visualization of theair flow patterns established by the blower fan.

A microcontroller may be used to control either the blower fan oracoustic transformer. One exemplary microcontroller that may be used inaccordance with the invention is the Arduino® microcontroller fromAdafruit Industries, New York, N.Y., though the invention is not limitedto any particular microcontrollers or associated software. In-housedeveloped firmware allowed for control of various fan or transformerfunctions, including: blower speed, fan blade rotation direction,continuous or alternating fan rotation direction, ultrasonic waveintensity, and synchronization with a rotating coupon platform. It willbe appreciated that a general purpose controller may be used, and thatthe controller may be programmed to carry out these or other functions.

Coupon Platform

One or more test coupons used in accordance with the invention may beheld in a stationary position in order to allow particles from the duststorm apparatus to be deposited thereon. In other aspects, the one ormore test coupons may be held on a moving platform in order tocompensate for any lack of uniformity in depositing particles during thedust storm process. The moving platform may be a rotating platform, andmore preferably, the rotation speed of the moving platform may becontrolled using a processor. The processor may be programmed to permita user to vary the rotation speed. Alternatively, the processor may beprogrammed so that the rotation speed is adjusted automatically based oninformation regarding the particles (such as density and size), theairflow speed and direction within the apparatus, the detection ofparticle flux non-uniformities, and the loading level of the coupon orcoupons, beneficially permitting end result-controlled test couponfabrication that achieves specific desired particle size and arealcoverage parameters.

Feedback Control

Another aspect of the invention includes different feedback controlmechanisms to allow the dust storm process to be automatically haltedwhen a target loading has been reached. An optical in situ measurementor in situ miniature resonating device such as a quartz crystalmicrobalance (QCM) or related surface acoustic wave (SAW) sensor mayprovide the capability to halt the deposition process when a desiredparticle loading has been achieved on one or more of the coupons.Because there is normally more than one coupon being coated, one couponcan serve as a witness coupon that is continuously monitored. Thisaspect of the invention can be particularly useful when the witnesscoupon is a glass microscope slide and the other coupons are substrateswhich are too rough or provide too poor particle viewing capability tobe considered for visible microscopy characterization. When provided, awindow or windows may preferably be formed in the lid or containerhousing the coupons, in order to provide a view of at least one coupon.Another approach could include a miniaturized digital camera unit withcorresponding optics (for example, a magnifying lens system) embeddedinto the coupon holder base to allow direct monitoring of particlesdeposited by looking through a glass coupon during the particle loadingprogress.

Regardless of the mechanism used to detect the particle loading, thedust storm process may be halted, for example, by stopping the blowingof the particles or ultrasonic wave transmission (e.g., by turning offthe fan/blower or acoustic transformer), or by deploying a mask toprevent deposition of further particles on the coupons after a desiredloading has been reached.

Laser-Assisted Deposition of Selected Particles

Coupons having particles of interest deposited thereon may bebeneficially used in further apparatus and methods. In one preferredembodiment of the invention shown in FIG. 16, the particles 4314deposited on a coupon 4312 may be individually visualized by acquiringan image of a loaded coupon (for example, using a high resolution cameraor microscope 4200 with a 20× reflecting objective 4210 that reflectsthe image off of mirror 4220), displaying the image on a display orprinted image 4230, and cataloguing the position and size of eachparticle using existing image processing techniques. Once the particleshave been catalogued, specific particles of interest 4324 may beindividually identified for further processing.

In one aspect, individual particles of interest (identified based ontheir shape, size, composition, or other considerations) may be removedfrom the coupon 4312 by utilizing a pulse from a laser 4100 to generatea mini shock wave in the coupon in the area where the individualparticle being removed is located. Lasers suitable for use in the LSDtechnique include gas lasers (e.g., CO₂ lasers), solid-state lasers(e.g., YAG lasers), and any other laser suitable for use in dislodgingparticles of interest from a coupon without altering the particles ofinterest or the particles in the areas surrounding them. In some aspectsof the invention, pulsed CO₂ lasers are preferred. The energy of the CO₂laser is absorbed by the top surface of the loaded glass coupon (i.e.,the side not coated with particles), so no laser damage occurs to theparticles or the optional glass optics that may be used to guide thestages. In some aspects of the invention, more than one laser may beprovided to increase throughput.

The shock from the activation of the laser causes the particle ofinterest 4324 to fall off of the coupon 4312 and onto a second coupon orother substrate 4322. A mask 4330 may optionally be provided to preventunintended deposition of particles on the second coupon, for example, ifthe laser dislodges a neighboring particle at the same time that theparticle of interest is dislodged, or if the particle of interestdeviates from its expected path when falling from the first coupon.Receiving substrates prepared in this manner may beneficially be usedfor calibration or testing of standoff detection apparatus.

The technique is agnostic towards the receiving substrate, and exemplarymaterials for use as receiving substrates include glasses used inconsumer electronics or automobile applications; silicate glasses, suchas soda lime glass and borosilicate glass; metals; painted metals; wood;paper; cardboard; and woven cloth of all material types and wovenconfiguration. A wide range of polymers may also be used as receivingsubstrates in accordance with the invention, such aspolymethylmethacrylate, polystyrene, Bakelite, polyvinylchloride, nylon,polyethylene terephthalate, polyurethane, polycarbonate, orpolyethylene. The loaded coupon having particles of interest thereon maybe formed using any material, and are preferably formed using materialsthat minimizes the area over which the shock wave caused by the laserbeam is transmitted. This reduces the likelihood that a particle locatednear the particle of interest will be dislodged from the loaded couponalong with the particle of interest. This may be accomplished by using amaterial that exhibits poor shock wave transmission, reducing thethickness of the coupon, or both.

The accuracy of particle deposition onto a receiving substrate whenusing the LSD technique may be improved by placing the first and secondcoupons 4312 and 4322 on moveable stages 4310 and 4320, so that thefalling particle 4324 lands at a designated coordinate on the receivingsubstrate 4322. The position of the first stage 4310 may be adjusted sothat the particle of interest 4324 is in the center of the field, wherethe laser is focused. Then the second stage 4320 with the receivingsubstrate 4322 is moved into position so that the particle of interest4324 free-falls directly down onto a desired location. The distancebetween the loaded glass coupon and the target substrate is preferablyminimized so that no significant X-Y deviation occurs during particlefree-fall. The atmosphere surrounding the first and second stages 4310and 4320 may be controlled to prevent air currents or temperaturegradients from influencing the particle of interest as it falls from theloaded coupon to the receiving substrate, and in some aspects, thiscontrol may include applying an electric field to the coupon andreceiving substrate to minimize deviations during particle free-fall. Insome aspects of the invention, the stages may be part of the opticalvisualization apparatus 4200, such as a microscope, which may be used toidentify particles of interest. Additionally a mask may be used (notshown) between loaded coupon 4312 and receiving substrate 4322 to ensureonly the intended particle 4324 has line of site to the receivingsubstrate 4322 and other particles 4314 cannot land on receivingsubstrate 4322 if one or more also happen to become dislodged from theloaded coupon. In those aspects of the invention where multiple lasersare used, multiple sets of first and second stages and/or rotating setsof first and second stages may be used to deposit particles on multiplereceiving substrates.

In order to print a pattern using the particles 4314 provided onsubstrate 4312, there is no limit to the number of times that the lasermay be activated in order to remove a particle of interest 4324 from thesubstrate 4312 to cause it to be deposited on a desired location oftarget 4322. While printing the target 4322, if particles of a certaindesired type become exhausted in the image of the loaded glass coupon4312, the invention beneficially permits the printer to move the firststage to a different part of the glass coupon, or load a new stockcoupon into the first stage and repeat the image analysis, in order tocontinue printing particles on the same target coupon loaded into thesecond stage. Any number of particles may be deposited in any desiredpattern using this aspect of the invention.

This Laser Shock Deposition (LSD) technique can also be used to removeindividual particles that are not of interest from a coupon. Theparticles selected for removal may have a shape, size, composition, orother feature that is not desired, leaving only the particles ofinterest on the coupon.

The receiving substrate may optionally be pre-treated to have acomposition present on its surface, such as a layer or pattern ofbackground material that may be present in an environment where theparticle of interest is to be detected. For example, a pattern mimickinga fingerprint may be deposited using sebum, sweat, or sebum/sweatderived compounds on the receiving substrate, and one or more particlesof interest may be knocked off of the coupon and onto a specificlocation on the receiving substrate. The coupons prepared in this mannermay beneficially be used for calibration of standoff detectionapparatus. It is also envisioned that a layer of fabric, lint, hair, orother material could be provided on substrate 4322 to mimic anenvironment where particle 4324 is to be detected.

The LSD system of the invention may be used in accordance with a methodfor custom printing substrates with particles of interest. The patternsin which the particles may be deposited are unlimited, and can beadjusted to suit the use for which the substrate is being prepared. Forexample, in order to test standoff detection equipment, patternsmimicking fingerprints, footprints, smudges, smears, or other effectsmay be used. In some aspects, the particles may be printed in a uniformpattern, such as a grid. The particles may be loaded in graduatedamounts to produce a set of calibration standards, which may be used toquantify the amount of a particular particle present in an unknownsample, or to aid in determining lower limits of detection for aparticular standoff detection apparatus.

The coupons prepared using the LSD apparatus and method described hereinmay beneficially be used for calibration or testing of standoffdetection apparatus, which may be used in determining the presence orabsence of particulate materials found in explosives, chemical orbiological weapons, narcotics, or environmental pollutants. They mayalso be used for evaluating pharmaceuticals, cosmetics, cementmaterials, ink components, food substances (including, withoutlimitation, sugar and flour), contaminants of any of these materials,and any other compositions that are supplied or may be detected inpowder or particulate form. Additional applications are envisionedwithin the scope of the invention.

EXAMPLES

The invention will now be particularly described by way of example.However, it will be apparent to one skilled in the art that the specificdetails are not required in order to practice the invention. Thefollowing descriptions of specific embodiments of the present inventionare presented for purposes of illustration and description. They are notintended to be exhaustive of or to limit the invention to the preciseforms disclosed. Many modifications and variations are possible in viewof the above teachings. The embodiments are shown and described in orderto best explain the principles of the invention and its practicalapplications, to thereby enable others skilled in the art to bestutilize the invention and various embodiments with various modificationsas are suited to the particular use contemplated.

Example 1

In order to test a sieving assembly incorporating a wiper blade therein,a sieving apparatus was fitted with a wiper blade that revolved at 50rpm. The rotating coupon holder was fitted with four 1″×1″ square glasscoupons, and a mask having four 0.8″×0.8″ square openings was appliedover the coupon holder and coupons.

A sieve with 20 micron openings and containing a prefractionated load offrom 0 to 38 microns was used, and sieving was carried out for 3 minutesto a coupon load of 30 micrograms/cm². Wiper blade sieving results in10-20 times greater particle throughput as compared to sieves notincorporating a blade that contacts the sieving membrane, and preventsor reduces particle pooling. Use of the rotating coupon platform furtherevens out particle distribution. The vibration isolation provided by therubber feet between the base of the rotating coupon platform and thecollection pan limits particle redistribution after deposition on thecoupons.

No vibratory or impact hammer assistance was used, and adequate particleuniformity across the multiple coupons was achieved by this system. Anexample of particle deposition on a coupon by sieving is found in FIG.17B.

Example 2

In one implementation of the mechanical decoupling technique, customcylindrical-shaped rubber feet were fabricated. The feet were designedto friction fit into 4 matching notches machined in the bottom side ofthe coupon holder and to protrude to lift the coupon holder away fromthe floor of the collection pan and enable the coupon holder tooscillate horizontally (shear mode). The friction fit design allows foreasy cleaning and replacement for applications operating in a differentfrequency domain. It was found that the four feet provide suitablestability for the coupon holder while the vibration sieving operationwas carried out.

The polymers considered for fabricating the feet were based on productsfrom Smooth-On, Inc., of Macungie, Pa. In this comparative analysis, theSmooth-On, Inc. products Ecoflex® 00-30 and Dragon Skin® 20 werecompared. Ecoflex® 00-30 has a Shore hardness of 30 based on the ShoreOO scale. This hardness is comparable to the hardness of the fleshy partof a normal healthy human fingertip. Dragon Skin® 20 is firmer and has aShore hardness of 20 on the Shore A scale. The cylindrical feet werecast in custom-made molds and were fabricated with the dimensions of24/64 inch height and ½ inch diameter.

After placing the completely assembled coupon holder with four Ecoflex®00-30 rubber feet on the sieve collection pan, we observed the followingduring sieving procedures:

-   -   Removal or absorption of any large amplitudes in the coupon        holder originating from the vibrating sieve stack.    -   Weakening of any vibration amplitude to a lower level.    -   No increase above the natural frequency at different set        vibration frequency levels.        These observations were made subjectively by contacting the        coupon holder with a finger.

The feet fabricated using Dragon Skin® 20 were found to be too firm. Thehard amplitude from the vibrating sieve stack was substantiallytransmitted through to the coupon holder and there was almost noweakening or absorption observed in the coupon vibration characteristicsusing the finger test.

Initial sieving tests conducted using the Ecoflex® 00-30 feet resultedin improved particle distribution (uniformity) across the entire couponholder surface.

Example 3

The dust storm deposition technique is illustrated in FIG. 14. Thesystem consists of a cylindrical container, an electrical fan (withpower supply and controller), an appropriate substrate holder and theparticles to be deposited on the substrate or coupon(s). The fanestablishes a cyclonic airflow within the container which drives micronsized particles in a circular motion, and then lifts them up towards thetop of the container where the particles adhere to one or more coupons.

The glass jar selected in the preliminary experiment described here wasselected for convenience and to allow easy visual observations. The fanselected was a simple vane axial fan. The direction of the air flow wasdirected downwards towards the bottom of the glass jar. The rotationaldirection of the fan can be ignored. The two wires for power supply plusan additional wire without functionality held the fan in position. Thelid of the jar contains a simple substrate holder which allows easymounting and dismounting of a test coupon.

The first dust storm experiment did not incorporate the ball millprocess and simply used material ground up with pestle and mortar andtransferred into the glass jar. This test did not employ particles ofcertain fractionated size but still contained the target size between 1and 30 microns (for fingerprint type particles). It also did not preventparticles from agglomerating together. But it was assumed there wereenough small single particles which would adhere as desired to thecoupon substrate. To break up possible agglomerations polyethylene (PE)beads were included with the particles. The PE beads where lightweightenough to flow with the particles and additionally allowed the air flowpatterns to be more observable.

After turning on the fan, for approximately 10 seconds in total, acyclonic airflow was observed through the movement of the PE beads. Aclose-up was filmed at 240 fps which afterwards confirmed that theparticles followed the same cyclonic motion. The particles and beadswere initially observed to rotate on the bottom of the jar, and afterthe cyclone was more established the particles and beads were liftedupwards while still rotating around the long axis of the container.

The coupon substrate was photomicrographed after the experiment.Analyses using Particle Math (developed by the U.S. Naval ResearchLaboratory, Washington, D.C.) established that the coverage achieved wasabout 2.5 μg/cm² and the effective diameters for the deposited particleswere in the range of 1.4 to 25.8 μm. Particle distribution over theentire glass coupon was observed, shown in FIG. 17A. In addition, highparticle adhesion was observed on all of the glass jar surfaces.

This initial dust storm experiment was deemed successful because itdeposited the particle sizes of interest quickly and in a uniformfashion across the entire coupon. It may be possible that the dust stormapparatus operated in this experiment helped to filter or prevent largerparticles from adhering to the coupon.

Example 4

A canister used in ball milling may be expanded with an interchangeablelid, to which is attached the fan blower and coupon holder from thepreliminary dust storm study with a glass jar.

The fan was secured by 3 metal rods and a ring holder, which allowed thefan to be placed in different positions, as shown in FIG. 15. The couponrested on a gasket on the outside of the lid and the can. Thisimprovement allowed for a simple, quick exchange of coupons. The openingin the lid, which enables the particle deposition onto the coupon, isnot limited in size or shape. The gasket prevents the substrate fromresting directly on the lid surface and additionally prevents particlesfrom escaping the can while the fan blower is being operated.

The same can used to mill particles is employed for dust stormgeneration by swapping out the lid for one with the fan blower andcoupon assembly after ball milling. The freshly ground up materialtogether with the ball bearings remain together inside the can duringthe dust storm. After the lid had been exchanged, the particledeposition via the dust storm was initiated. Depending on the amount ofharvested, ground particles within the can, multiple coupons can becoated with particles.

This setup can be easily equipped with a dry air support, but that wasnot included in this example.

All parts within the can are covered with the ground up particles afterthe dust storm deposition.

A good distribution of particles across the coupon was observed, butthere was also one problem identified. In one certain area the loadingwas much higher than in the rest. This was likely due to the thicknessof the gasket used to secure the coupon, which allowed an airflowshadow. The coupons should be mounted as flush to the lid as possible toavoid additional turbulence that impacts the particle distribution onthe coupon.

Example 5

In order to test a laser deposition apparatus, a blank substrate wasplaced beneath an upside-down glass coupon that included a high loadingof particles (50-100 micrograms/cm²). As a first step, an image of theglass coupon was taken and processed in situ, and the position and sizeof all particles on the coupon were catalogued. This image forms theparticle stock from which particles can be printed on the blank glasssubstrate.

Desired particles were selected using the image of the glass coupon.Particles may be selected based on size, shape, or other considerations.

XY coordinates on the blank substrate where each particle should bedeposited were then selected. For each selected particle, the firststage holding the loaded glass coupon was moved so that the particle isin the center of the image, where the laser is focused. Then, the secondstage holding the blank substrate is moved to position the location onthe blank where the particle is to be deposited directly beneath theparticle on the first stage.

A CO₂ laser pulse was aimed at the location on the loaded coupon wherethe particle of interest was located, and fired to generate a miniatureshock wave that travels to the other side of the glass coupon, knockingthe particle of interest off of the loaded coupon. The particlefree-falls onto the blank target substrate. Particle transfer wasobserved on the receiving substrate after the laser shock depositionprocess.

The CO₂ laser is absorbed by the top surface of the glass coupon, so nolaser damage occurs to the particles or the glass optics used to guidethe system. The distance between the loaded glass coupon and the targetsubstrate is kept small so that no significant XY deviation occursduring freefall.

If particles of a certain type become exhausted in the image of theglass coupon, it is possible to move to a different part of the glasscoupon, or load a new stock coupon into the device and repeat the imageanalysis, and continue printing on the same target coupon.

It will, of course, be appreciated that the above description has beengiven by way of example only and that modifications in detail may bemade within the scope of the present invention.

Throughout this application, various patents and publications have beencited. The disclosures of these patents and publications in theirentireties are hereby incorporated by reference into this application,in order to more fully describe the state of the art to which thisinvention pertains.

The invention is capable of modification, alteration, and equivalents inform and function, as will occur to those ordinarily skilled in thepertinent arts having the benefit of this disclosure. While the presentinvention has been described with respect to what are presentlyconsidered the preferred embodiments, the invention is not so limited.To the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the description provided above.

What is claimed:
 1. A sieving apparatus, comprising: a sieving panadapted for receiving particles to be sieved, comprising: a sievemembrane having upper and lower surfaces; and a wiper that wipesparticles over the upper surface of the sieve membrane; a collection panthat retains particles that pass through the sieve membrane; and asubstrate provided within the collection pan to receive a portion of theparticles that pass through the sieve membrane; wherein the wiper ismoved with respect to the upper surface of the sieve membrane andapplies force to particles adjacent to the upper surface of the sievemembrane, producing particle distributions that are on averagesubstantially uniform across the width of the wiper and accelerating themovement of the particles through openings in the sieve membrane intothe collection pan and onto the substrate.
 2. The apparatus of claim 1,further comprising a vibration generator that generates vibratory actionto cause particles to pass through the sieve membrane.
 3. The apparatusof claim 1, wherein the wiper is in contact with the upper surface ofthe sieve membrane.
 4. The apparatus of claim 1, wherein the wiper isselected from the group consisting of a blade, a segmented blade, and abrush.
 5. The apparatus of claim 4, wherein the segmented blade issegmented into strips that flail as said segmented blade is rotatedagainst the sieve membrane, randomizing the contact of said strips withthe sieve membrane.
 6. The apparatus of claim 4, wherein the brushcomprises fibers configured to form one or more brush assemblies thatflex as said brush is rotated against the sieve membrane, randomizingthe contact of said fibers with the sieve membrane.
 7. The apparatus ofclaim 1, wherein the sieving pan and collection pan are provided in adry atmosphere.
 8. The apparatus of claim 1, wherein the sieving pan andcollection pan are mechanically coupled, such that when vibration isapplied to the collection pan, the vibration is transmitted to thesieving pan.
 9. The apparatus of claim 1, wherein the collection pan hasa coupon platform provided therein, and wherein the coupon platformcomprises a coupon holder adapted to receive one or more test couponsthereon.
 10. The apparatus of claim 9, wherein the coupon platformcomprises a vibration damper.
 11. The apparatus of claim 1, wherein thesieving apparatus comprises actuators for preventing particles fromblocking the sieve membrane.
 12. The apparatus of claim 11, wherein theactuators are selected from a tamping device positioned above a lidprovided on the sieving pan, and one or more ultrasonic actuatorspositioned around the sieve membrane.
 13. The apparatus of claim 1,wherein the collection pan comprises a sensor to provide real timemonitoring of particle mass depositions and provide a feedback controlmechanism.
 14. The apparatus of claim 1, wherein the collection pancomprises an observation window comprising an optically transparentmaterial, and a camera or optical microscope positioned to viewparticles landing on the observation window or on an opticallytransparent witness coupon viewable through the window.
 15. Theapparatus of claim 14, wherein the observation window comprises anoptically transparent witness coupon included among one or more couponsnot suitable for optical analysis, and a level of particle loading onthe witness coupon is used to estimate particle loading on the one ormore coupons not suitable for optical analysis.
 16. The apparatus ofclaim 1, further comprising a controller for adjusting speed, duration,and direction of rotation for the wiper.
 17. A sieving apparatus,comprising: a sieving pan adapted for receiving particles to be sieved,comprising a sieve membrane having upper and lower surfaces; a vibrationgenerator that generates vibratory action to cause particles to passthrough the sieve membrane; a collection pan that retains particles thatpass through the sieve membrane; and a rotating coupon stage having asurface adapted to receive one or more coupons, where the one or morecoupons receive a portion of the particles that pass through the sievemembrane; wherein the coupon stage is provided in the collection pan,and is rotated as the particles are sieved, producing particledistributions that are more uniform across the one or more coupons whencompared to particle distributions produced on coupons that are notrotated during sieving.
 18. The apparatus of claim 17, wherein thecoupon stage surface is rotated in a circular orbit.
 19. The apparatusof claim 17, further comprising an electric motor configured to rotatethe coupon stage surface.
 20. The apparatus of claim 17, wherein adamper is provided between the rotating coupon stage and the surface ofthe receiving pan.